An integrated series of experiments are proposed to continue studies on the molecular genetics of the mammalian brain. Emphasis is placed on investigation of nonpolyadenylated (poly A)-)mRNAs from the brain with respect to specificity, biogenesis, regulation and expression of respective genes during postnatal development. The poly(A)- mRNAs are of particular interest because they constitute a complex population of sequences, nonhomologous with polyadenylated (poly(A)+)mRNAs, and they are encoded in genes which are mostly expressed after birth. Also, initial data indicates the brain poly(A)-mRNAs are unique to that organ and their respective genes appear to be regulated tightly at the transcriptional level. We proposed to define the nuclear precursors and the general code sequence arrangement in the DNA (continuous or discontinuous) for poly (A)-mRNAs. Distribution of poly(A)-mRNAs in different anatomical regions and in different major cell types will be charted. The time course (late fetus to young adult) of the expression of genes specifying brain poly(A)-mRNAs will be defined. We have identified poly(A)+mRNAs which are specific to the brain, relative to liver and kidney polysomal RNA. However, some of these mRNA sequences are present in the nuclear RNA of liver or kidney. We propose experiments to determine whether such leaky or constitutive transcription of inactive genes (genes not represented by mRNA in polysomes) may be due to their close linear relationship with active genes. To accomplish various phases of our investigation we will use complex cDNA and mDNA probes, and genomic and cDNA clones. Our research requires the isolation and pulse labeling of nuclei and fractionation of various size classes of nuclear RNA. A large number of different "types" of DNA/RNA hybridizations will be performed. Cloned probes can be used to obtain relatively precise information despite the immense cellular complexity of brain. Our results should significantly advance our knowledge and provide a foundation for future, more dynamic studies. One such future aspect might be to determine whether genes expressed postnatally are influenced by environmental inputs and, if so, are there critical periods for the expression of these genes.